Electrochromic devices and methods

ABSTRACT

A heat treated electrochromic device comprising an anodic complementary counter electrode layer comprised of a mixed tungsten-nickel oxide and lithium, which provides a high transmission in the fully intercalated state and which is capable of long term stability, is disclosed. Methods of making an electrochromic device comprising an anodic complementary counter electrode comprised of a mixed tungsten-nickel oxide are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/359,664, filed on Feb. 22, 2006, and claims the benefit of the filingdate of U.S. Provisional Patent Application No. 60/655,578 filed Feb.23, 2005, the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to electrochromic devices which can vary thetransmission or reflectance of electromagnetic radiation by applicationof an electrical potential to the electrochromic device.

Certain materials, referred to as electrochromic materials, are known tochange their optical properties in response to the application of anelectrical potential. This property has been taken advantage of toproduce electrochromic devices which can be controlled to transmitoptical energy selectively.

A number of factors affect the operation of an electrochromic device.One limitation on how dark an electrochromic device can become is howmuch charge can be stored in the counter electrode layer. There havebeen many different approaches for producing a charge storage medium,but most attention has focused on a thin film deposited parallel to theelectrochromic material layer, and separated by an ionically conductivelayer.

To date, most counter electrode layers have been made using NiO, LiNiO,or doped variants thereof. One advantage of using NiO and LiNiOmaterials is that under careful preparation conditions, the counterelectrode can be made so that it displays anodic electrochromism withgood efficiency and a high bleached state transmission. Unfortunately,it has been difficult to intercalate lithium into NiO based materials asa result of the material's compact crystalline structure. As such,higher voltages must be applied to such materials to intercalatelithium, which leads to undesirable side reactions.

Other methods employ proton coloration based mechanisms utilizingcounter electrode layers comprised of vanadium oxides and other mixturescontaining vanadium. Although it may be relatively easy to manufacture acounter electrode layer capable of coloring anodically in an aqueousmedium, it is difficult to produce a complete device capable oflong-term stability. It is, therefore, more advantageous to use lithiumintercalation based systems.

A typical material used for counter electrode applications with lithiumis vanadium oxide, which is a material that forms crystal structuressimilar to those seen in tungsten oxide systems. The open crystallinelattice of vanadium oxide allows lithium intercalation more readily thanin NiO based structures. However, the presence of vanadium ions leads tothe generation of a strong yellow color. This yellow color is onlyslightly modulated by lithium intercalation, and shows a reasonablecathodic electrochromic effect throughout the majority of the visibleregion, thus limiting the maximum transmission that can be achievedusing this material as a counter electrode layer. Attempts to reduce thedegree of coloration by doping vanadium oxides with other componentsresult in a reduced electrochromic efficiency by reduction of the chargecapacity of the counter electrode layer. Such doping results in a devicewith a higher bleached state transmission at the cost of a highercolored state transmission.

The problems associated with current counter electrode practice can besummarized with reference to FIG. 1, which provides an illustration ofcoloration in an electrochromic device having a cathodic counterelectrode layer. The overall dynamic range for such a device is given bythe net optical density change upon transferring charge from the counterelectrode to the electromatic material layer. Such a transfer of chargeresults in a loss of optical density from the counter electrode and again of optical density in the electrochromic material layer. Hence, thenet change in optical density is given by the difference inelectrochromic efficiency between the electrochromic material layer andthe counter electrode. Condition 1 shows a lower overall level of chargeand, thus, a lower initial bleached state as compared with Condition 2.On the other hand, Condition 2 shows the situation when the chargecapacity is increased, such as by increasing the thickness of thecounter electrode layer. As a result, there is an increase in theoverall dynamic range along with a concomitant increase in the opticaldensity seen in the bleached state. Therefore, while the total charge ofa cathodic counter electrode layer may be increased to enhance theoverall dynamic range of the device, the optical density of the counterelectrode also increases resulting in a less transparent bleached state.

Devices employing anodic counter electrodes have been briefly discussedin the prior art. Some of these devices employ counter electrodescomprised of nickel oxides doped with tungsten or tantalum. However, thematerials comprising such counter electrodes contain the metal oxide inan amorphous phase. As a result, such devices suffer from low colorationefficiencies and low conductivity.

In view of the above problems, there remains a need for improvedelectrochromic coatings, and in particular electrochromic coatings thatcomprise solid state, inorganic thin films, and metal oxide thin films.In addition, there remains a need for electrochromic coatings thatincorporate complementary anodic and cathodic electrochromic ioninsertion layers, whose counter ions are either protons or lithium ions.There also remains a need for improved methods for making complementaryelectrochromic layers to act as a counter electrode, having improvedproperties over existing practices. Further, there also remains a needfor an electrochromic device with a suitably wide transmission rangebetween fully colored and fully bleached states, with suitably fastcoloration and bleaching rates, and with suitable longevity anddurability for outdoor architectural applications.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been realized by the discovery of an electrochromic devicecomprising an anodic complementary counter electrode comprised of amixed tungsten-nickel oxide and lithium. As such, the electrochromicdevice of the present invention is comprised of five sequential layersincluding two conductive layers, an electrochromic layer, an ionconductor layer, and an anodic complementary counter electrode layer.

In accordance with one embodiment of the electrochromic device, theamount of nickel present in the mixed tungsten-nickel oxide ranges fromabout 15% to about 90% by weight of the mixed oxide. Preferably, theamount of nickel ranges from about 30% to about 70% by weight of themixed oxide. Most preferably, the amount of nickel ranges from about 40%to about 60% by weight of the mixed oxide.

In accordance with another embodiment of the electrochromic device, theelectrochromic layer is comprised of a metal oxide. In a preferredembodiment, the metal oxide is selected from tungsten oxide, molybdenumoxide, niobium oxide, titanium oxide, copper oxide, iridium oxide,chromium oxide, and manganese oxide. More particularly, the metal oxideis tungsten oxide. In other embodiments, the metal oxide may be dopedwith one or more metals.

In accordance with another embodiment of the electrochromic device, theconductive layers are comprised of a metal oxide. In a preferredembodiment, the metal oxides of the conductive layers are selected fromindium oxide, tin oxide, zinc oxide, and systems based on silver whichare well known in the glazing industry. In some embodiments, the metaloxide is doped with one or more metals. More particularly, the metaloxide is indium tin oxide. The electrochromic device of the presentinvention comprises two conductive layers. As such, each of theconductive layers may be comprised of the same materials or differentmaterials.

In accordance with another embodiment of the electrochromic device, theion conductor layer is comprised of a lithium-ion conducting layer.Preferably, the lithium-ion conductor layer is comprised of a materialselected from the groups consisting of silicates, silicon oxides, andborates.

In accordance with another embodiment of the electrochromic device, theanodic complementary counter electrode has a substantially uniformthickness ranging from about 500 Angstroms to about 6500 Angstroms.Preferably, the thickness ranges from about 1500 Angstroms to about 2500Angstroms.

In accordance with the present invention, a method has also beendiscovered for preparing an electrochromic device deposited on asubstrate comprising the steps of depositing one of an electrochromiclayer or a counter electrode layer comprised of a mixed tungsten-nickeloxide on a first conductive layer, thereby providing a first depositedelectrode, depositing an ion-conductor layer on the first depositedelectrode, depositing the other of the electrochromic layer or thecounter electrode layer on the ion-conductor layer, thereby providing asecond deposited electrode, depositing a second conductive layer on thesecond deposited electrode, and heating the electrochromic device,whereby the mixed tungsten-nickel oxide is reduced through deposition oflithium onto the counter electrode layer immediately following itsdeposition. In one embodiment, the amount of nickel in the mixedtungsten-nickel oxide ranges from about 15% to about 90% by weight ofthe mixed oxide. In another embodiment, the amount of nickel ranges fromabout 30% to about 70% by weight of the mixed oxide. In a preferredembodiment, the amount of nickel ranges from about 40% to about 60% byweight of the mixed oxide.

In accordance with another embodiment of the method of the presentinvention, lithium is deposited onto the counter electrode in an amountwhich provides a maximum transmission through the counter electrode. Inanother embodiment, the amount of lithium deposited onto the counterelectrode will be in excess of the amount which provides a maximumtransmission through the counter electrode. More particularly, theexcess amount of lithium deposited ranges from about 10% to about 40%above the amount which provides a maximum transmission through thecounter electrode.

In accordance with another embodiment of the method of the presentinvention, the electrochromic device is heated to a temperature rangingfrom about 280° C. to about 500° C. In a preferred embodiment, theelectrochromic device is heated to a temperature ranging from about 355°C. to about 395° C.

In accordance with another embodiment of the method of the presentinvention, the anodic complementary counter electrode layer is depositedby means of physical vapor deposition. More particularly, the anodiccomplementary counter electrode layer is deposited by means ofintermediate frequency reactive sputtering or DC reactive sputtering.

In accordance with another embodiment of the method of the presentinvention, lithium is deposited on the anodic complementary counterelectrode by means of wet chemical methods or by means of physical vapordeposition. In particular, the lithium may be deposited by means ofintermediate frequency reactive sputtering or DC sputtering.

Yet another aspect of the present invention is to provide a method ofmaking a counter electrode layer for use in connection with anelectrochromic device comprising the steps of depositing a film of amixed tungsten-nickel oxide on a substrate, reducing the mixedtungsten-nickel oxide film by depositing lithium on the film, andheating the counter electrode layer.

Applicants have found that an electrochromic device utilizing an anodiccounter electrode comprised of a mixed tungsten-nickel oxide provides asuitably wide transmission range between the fully colored and fullybleached states. Moreover, such a device has found to be capable ofreversibly intercalating several tens of millicoulombs per squarecentimeter of charge in the form of ions and charge compensatingelectrons. Further, applicants have discovered that an anodic counterelectrode comprised of a mixed tungsten-nickel oxide provides acomplementary response upon insertion of charge. Finally, applicantshave discovered that an electrochromic device employing such a mixedtungsten-nickel oxide has improved transmission in the lithiated counterelectrode layer when such device is heated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph detailing the coloration of an electrochromic devicehaving a cathodic counter electrode layer.

FIG. 2 is a graph detailing the coloration of an electrochromic devicehaving an anodic counter electrode layer.

FIG. 3 is a schematic cross-section of a five layer electrochromicdevice in accordance with one embodiment of the current invention.

FIG. 4 is a graph detailing the transmission level of a partiallycompleted electrochromic device during the deposition of lithium intothe anodic counter electrode.

DETAILED DESCRIPTION

One object of the present invention is to provide an electrochromicdevice having an anodic complementary counter electrode which provides ahigh transmission in the fully intercalated state and is capable of longterm stability suitable for use as a commercial product.

This and other objectives are realized by means of an electrochromicdevice utilizing an anodic complementary counter electrode comprised ofa mixed tugsten-nickel oxide which is capable of reversiblyintercalating several tens of millicoulombs of charge per squarecentimeter, in the form of lithium ions and charge compensatingelectrons, and that upon intercalation of such ions, results in a hightransmission in the fully intercalated state.

Another objective of the present invention is to provide a method ofpreparing an anodic complementary counter electrode layer for use inconnection with an electrochromic device comprising a mixedtungsten-nickel oxide.

Another objective of the present invention is to provide a method ofpreparing an electrochromic device comprising an anodic complementarycounter electrode comprised of a mixed tungsten-nickel oxide.

The shortcomings of the prior art, particularly those associated withcathodic counter electrodes (i.e. having to choose between a widedynamic range or a counter electrode having a high bleached statetransmission), are overcome through the use of an anodic complementarycounter electrode as described herein. The dynamic range of anelectrochromic device employing such an anodic complementary counterelectrode allows the device's dynamic range to be increased simply byincreasing the amount of charge transferred, provided the amount ofcharge in the counter electrode is controlled well enough to maintainhigh transparency.

FIG. 2 illustrates the coloration of an electrochromic device utilizingan anodic complementary counter electrode layer having an increaseddynamic range and a high initial bleached state in comparison to acathodic counter electrode. Unlike in FIG. 1, the dynamic range in FIG.2 is given by the sum of the electrochromic efficiencies of the counterelectrode and the electrochromic material layers. The net result is thatthe dynamic range may be increased simply by increasing the amount ofcharge transferred to the anodic complementary counter electrode layer.Condition 1 and Condition 2 are different in that the anodic counterelectrode in Condition 1 holds a lower amount of charge as compared withthe anodic counter electrode in Condition 2. However, the lower amountof charge in Condition 1 as compared with Condition 2 does not lead to acompromise in the bleached state optical density. Increasing thethickness of the anodic counter electrode, as demonstrated by Condition2, increases the overall dynamic range of the device without changingthe initial bleached state optical density.

Prior to describing the invention further, some definitions will behelpful.

As used herein, the term “bleached state” means the state of anelectrochromic material that is at least partially clear or at leastpartially non-colored.

As used herein, the term “intercalation” means the reversible insertionof a molecule, atom or ion into a crystal lattice.

As used herein, the term “lithium” means elemental lithium, its salts,oxides, coordination complexes, and chelates. “Lithium” may also referto lithium ions.

As used herein, the term “sputtering” means a physical process wherebyatoms in a solid target material are ejected into the gas plasma phasedue to bombardment of the material by energetic ions. “Sputtering” willbe discussed with regard to its use in film deposition.

FIG. 3 shows a five layer electrochromic device in cross-section. Inorder for such a five-layer electrochromic device to function correctly,it is necessary to have at least the following sequential layers: anelectrochromic layer (“EC”) 30 which produces a change in absorption orreflection upon oxidation or reduction; an ion conductor layer (“IC”) 32which serves as an electrolyte, allowing the passage of ions whileblocking electronic current; a counter electrode (“CE”) 28 which servesas a storage layer for ions when the device is in the bleached state;and two conductive layers (“CL”) 24 and 26 which serve to apply anelectrical potential to the electrochromic device. Each of theaforementioned layers are applied sequentially on a substrate 34.

A low voltage electrical source 22 is connected to the device by meansof conductive wires. In order to alter the optical properties of window20, it is necessary that an electrical potential be applied across thelayered structure. The polarity of the electrical source will govern thenature of the electrical potential created and, thus, the direction ofion and electron flow. In the embodiment depicted in FIG. 3, theelectrical potential created will cause ions to flow from the counterelectrode layer 28 through the ion conductor layer 32 to theelectrochromic layer 30, thereby causing the electrochromic layer 30 totransform to the colored state thereby causing the transparency of thewindow 20 to be reduced.

The materials employed for the conductive layers 24 and 26 are wellknown to those skilled in the art. Exemplary conductive layer materialsinclude coatings of indium oxide, indium tin oxide, doped indium oxide,tin oxide, doped tin oxide, zinc oxide, doped zinc oxide, rutheniumoxide, doped ruthenium oxide and the like, as well as all thin metalliccoatings that are substantially transparent, such as transition metalsincluding gold, silver, aluminum, nickel alloy, and the like. It is alsopossible to employ multiple layer coatings, such as those available fromPilkington under the tradename of TEC-Glass®, or those available fromPPG Industries under the tradenames SUNGATE® 300 and SUNGATE® 500. Theconductive layers 24 and 26 may also be composite conductors prepared byplacing highly conductive ceramic and metal wires or conductive layerpatterns on one of the faces of the substrate and then overcoating thiswith transparent conductive materials such as indium tin oxide or dopedtin oxides. The conductive layers may be further treated withappropriate anti-reflective or protective oxide or nitride layers.

In some embodiments, the material selected for use in conductive layer26 is the same as the material selected for use in conductive layer 24.In other embodiments, the material selected for use in conductive layer26 is different than the material selected for use in conductive layer24.

Preferably, the conductive layers utilized in the present invention aretransparent layers of indium tin oxide. Typically, the conductive layer26 is disposed on a substrate having suitable optical, electrical,thermal, and mechanical properties such as, for example, glass, plasticor mirror materials, as a coating having a thickness in the range ofabout 5 nm to about 10,000 nm, and preferably about 10 nm to about 1,000nm. However, any thickness of the conductive layer may be employed thatprovides adequate conductance for the electrochromic device and whichdoes not appreciably interfere with the transmission of light whererequired. Moreover, conductive layer 24 is typically the final layer ofthe electrochromic device deposited on the counter electrode layer 28.Other passive layers used for improving optical properties, or providingmoisture or scratch resistance may be deposited on top of the activelayers. These conductive layers are connected to an electrical powersource in a conventional manner.

The electrochromic layer 30 employed as part of the present invention iswell known to those skilled in the art.

The electrochromic layer may be comprised of materials includinginorganic, organic blends and/or composites of inorganic and organicelectrochemically active materials such that the EC layer is capable ofreceiving ions transferred from the CE layer 28. Exemplary inorganicmetal oxide electrochemically active materials include WO₃, V₂O₅, MoO₃,Nb₂O₅, TiO₂, CuO, Ni₂O₃, Ir₂O₃, Cr₂O₃, Co₂O₃, Mn₂O₃, mixed oxides (e.gW—Mo oxide, W—V oxide) and the like. One skilled in the art wouldrecognize that each of the aforementioned metal oxides may beappropriately doped with lithium, sodium, potassium, molybdenum,vanadium, titanium, and/or other suitable metals or compounds containingmetals. In a preferred embodiment, the EC layer 30 is selected from WO₃or doped WO₃.

The thickness of the EC layer 30 may vary depending on theelectrochemically active material chosen. However, the EC layer 30typically ranges from about 500 Angstroms to about 20,000 Angstroms inthickness, preferably from about 3400 Angstroms to about 4200 Angstroms.

Overlying the electrochromic layer 30 is an ion conductor layer 32. Theion conductor layer 32 employed as part of the present invention iscomprised of a solid electrolyte capable of allowing ions to migratethrough the layer. The ion conductor layer 32 must have a sufficientionic transport property to allow ions, preferably lithium ions, tomigrate through. Any material may be used for an ion conductor providedit allows for the passage of ions from the counter electrode layer 28 tothe electrochromic layer 30. In some embodiments, the ion conductorlayer comprises a silicate-based structure. In other embodiments,suitable ion conductors particularly adapted for lithium iontransmission include, but are not limited to, lithium silicate, lithiumaluminum silicate, lithium aluminum borate, lithium borate, lithiumzirconium silicate, lithium niobate, lithium borosilicate, lithiumphosphosilicate, lithium nitride, lithium aluminum fluoride, and othersuch lithium-based ceramic materials, silicas, or silicon oxides. Othersuitable ion-conducting materials can be used, such as silicon dioxideor tantalum oxide. Preferably, the ion conductive layer 32 has low or noelectronic conductivity. The preferred ion conductor material is alithium-silicon-oxide produced by either sputtering or a sol-gelprocess.

The thickness of the IC layer 32 may vary depending on the material.However, the IC layer 32 typically ranges from about 100 Angstroms toabout 700 Angstroms in thickness, preferably from about 200 Angstroms toabout 600 Angstroms in thickness, and most preferably from about 325Angstroms to about 475 Angstroms in thickness.

The counter electrode layer 28 utilized in the electrochromic device ofthe present invention is an anodic complementary counter electrode. Thecounter electrode layer 28 is considered anodic because it is anodicallyelectrochromic, meaning that it will become more transparent whenreduced (i.e. when ions are intercalated), which is the opposite of morecommon electrochromic materials such as tungsten oxides. As a result ofthe counter electrode 28 being transparent in the charged state, thecounter electrode may act as a complementary electrochromic layer,causing the electrochromic device to color both from oxidation of thecounter electrode and reduction of the electrochromic layer 28. Thus,when charge (in the form of ions and electrons) is removed from thecomplementary counter electrode 28 of the present invention, the layerwill turn from a transparent state to a colored state.

The complementary counter electrode layer 28 of the present invention iscomprised of a mixed tungsten-nickel oxide capable of storing ions andthen releasing these ions for transfer to the electrochromic layer 30 inresponse to an appropriate electrical potential. In one embodiment, themixed oxide has the form of a Ni₂O₃ and WO₃ composite. In anotherembodiment, the amount of nickel present in the mixed tungsten-nickeloxide ranges from about 15% to about 90% by weight of said mixedtungsten-nickel oxide, preferably from about 30% to about 70% by weightof said tungsten-nickel oxide, and most preferably from about 40% toabout 60% by weight of said tungsten-nickel oxide. When charge isremoved from the mixed tungsten-nickel oxide, the CE layer 28 will turnfrom a transparent state to a brown colored state.

In some embodiments, the mixed tungsten-nickel oxide is present in anamorphous state. In other embodiments, the mixed tungsten-nickel oxideis present in a crystalline state. In yet other embodiments, the mixedtungsten-nickel oxide may be present in a mixed amorphous andcrystalline state. However, in preferred embodiments, the mixedtungsten-nickel oxide is present substantially in crystalline form.Without wishing to be bound by any particular theory, in some preferredembodiments, separate domains of different crystalline metal oxides maybe present as an admixture (i.e. an admixture of crystalline tungstenoxide and crystalline nickel oxide). Again, without wishing to be boundby any particular theory, in other preferred embodiments, separatedomains of a crystalline metal oxide and an amorphous metal oxide may bepresent (e.g. an admixture of amorphous nickel oxide and crystallinetungsten oxide, or an admixture of amorphous tungsten oxide andcrystalline nickel oxide).

The thickness of the complementary counter electrode layer 28 isvariable depending on the application sought for the electrochromicdevice and the transmission range desired. As such, the thickness mayrange from about 500 Angstroms to about 6500 Angstroms. In oneembodiment of the present invention, the thickness ranges from about1500 Angstroms to about 2500 Angstroms, preferably ranging from about1750 Angstroms to about 2050 Angstroms in thickness.

The complementary counter electrode layer 28 of the present invention isalso comprised of lithium. In one embodiment of the present invention,the lithium comprising the CE 28 is at least partially intercalatedwithin the mixed tungsten-nickel oxide. In another embodiment, thelithium is present as a film at least partially coating the surface ofthe CE. The lithium present in the CE 28, either on the CE surfaceand/or intercalated within the mixed tugsten-nickel oxide, is capable ofbeing reversibly transferred from the CE to the EC 30 when an electricalpotential is applied.

Typically the substrate 34 of the electrochromic device is comprised oftransparent glass or plastic such as, for example, acrylic, polystyrene,polycarbonate, allyl diglycol carbonate [CR39 available from PPGIndustries, Pittsburgh, Pa.], SAN [styrene acrylonitrile copolymer],poly(4-methyl-1-pentene), polyester, polyamide, etc. It is preferablefor the transparent substrate 34 to be either clear or tinted soda limeglass, preferably float glass. If plastic is employed, it is preferablyabrasion protected and barrier protected using a hard coat of, forexample, a silica/silicone anti-abrasion coating, a diamond-likeprotection coating or their like, such as is well known in the plasticglazing art. Generally, the substrates have a thickness in the range ofabout 0.01 mm to about 10 mm, and preferably in the range from about 0.1mm to 5 mm. However, any substrate of any thickness which will provide afunctioning electrochromic device may be employed.

It will be appreciated that the complementary counter electrode layer 28and the electrochromic layer 30 may be reversed in the overall structureof FIG. 3. However, if the CE layer 28 and the EC layer 30 are reversed,the polarity of the applied potential must be adjusted to ensure thatthe correct polarity for the layers is maintained.

In a preferred embodiment of the invention, the completed device of FIG.3 is subjected to a heat treatment process, carried out subsequent tothe fabrication of the device. A device subjected to such treatment hasimproved conductivity, an increased conductive layer transparency, andan increased transmission of the lithiated CE layer.

Moreover, when heated, the lithiated mixed tungsten-nickel oxide maytransform into a composite of Li₂WO₄ and Ni₂O₃.

The electrochromic device described herein could be coupled withradiation sensors (e.g., visible and solar) and energy managementsystems to automatically control their transmission and reflection.

The electrochromic device of the present invention may be powered withsolar cells, thermoelectric sources, wind generators, etc., to make themself-sustaining. These may be also coupled into charge storage devicessuch as batteries, re-chargeable batteries, capacitors or other means.The charge storage devices could be utilized as automatic backup powersource when primary source of power is interrupted.

The electrochromic device of the present invention may also be used asfilters in displays or monitors for reducing the ambient lightintensity, e.g., sun glare, that is incident on the monitor or displaysurface. Thus, the device may be employed to enhance the image qualityof displays and monitors, particularly in well lit conditions.

These electrochromic devices may also be used as displays having anadvantageously wide viewing area with a high contrast because nopolarizers are required as are in conventional liquid crystal displays

The electrochromic device of the present invention may also be used aseyewear or sunglasses.

A method of preparing an electrochromic device employing an anodiccomplementary counter electrode is also provided. A first conductivelayer 26 is deposited on substrate 34 by methods known in the art and inaccordance with the desired properties of a conductor layer aspreviously mentioned.

An electrochromic layer 30 is then deposited on conductor layer 26through wet chemical methods, chemical vapor deposition and/or physicalvapor deposition (e.g. sol-gel, metallo-organic decomposition, laserablation, evaporation, e-beam assisted evaporation, sputtering,intermediate frequency reactive sputtering, RF sputtering, magneticsputtering, DC sputtering, PVD and CVD and the like). In preferredembodiments, the electrochromic layer 30 is deposited via intermediatefrequency reactive sputtering or DC sputtering techniques. In oneembodiment, the EC layer 30 is deposited on a heated first conductorlayer 26.

The deposited electrochromic layer 30 may be comprised of metal oxidesincluding titanium oxides, vanadium oxides, tungsten oxides, molybdenumoxides, or doped variants thereof. In a preferred embodiment, theelectrochromic layer 30 deposited is comprised of WO₃. In someembodiments, the deposited WO₃ may contain a stoichiometric excess ordeficiency of oxygen, depending on the deposition method and conditionschosen. In other embodiments, the WO₃ may be doped with an appropriatemetal or metallic compound.

An ion conductor layer 32 is then deposited on EC layer 30 through wetchemical methods, chemical vapor deposition and/or physical vapordeposition (e.g. sol-gel, metallo-organic decomposition, laser ablation,evaporation, e-beam assisted evaporation, sputtering, intermediatefrequency reactive sputtering, RF sputtering, magnetic sputtering, DCsputtering, PVD and CVD and the like). In a preferred embodiment, theion conductor layer is deposited via a sol gel method or reactivesputtering.

An anodic complementary counter electrode layer 28 comprised of a filmof a mixed tungsten-nickel oxide is then deposited on the IC layer 32through physical vapor deposition, intermediate frequency reactivesputtering, DC sputtering, or RF-magnetron sputtering. In oneembodiment, tungsten chips are placed on a nickel target with thesputtering pressure set between 1 mTorr and 10 mTorr by introducingoxygen or argon into the chamber. In another embodiment, powderedtungsten-nickel metals or oxides are hot pressed or hot isostaticallypressed (HIPed) and utilized as a sputtering target in an oxygen rich orargon rich atmosphere.

After the deposition of the mixed tungsten-nickel oxide film, thetungsten-nickel oxide film is reduced through the deposition of lithium.The deposition of the lithium is achieved through one of either wetchemical methods, sol-gel, chemical vapor deposition, physical vapordeposition, or reactive sputtering. In a preferred embodiment, thesource of the lithium deposited on the tungsten-nickel oxide film islithium metal deposited in vacuum using a non-reactive sputteringprocess.

In one embodiment, the amount of lithium deposited on the mixedtungsten-nickel oxide film is carefully controlled such that an amountof lithium is added that allows for the greatest transmission of lightthrough the counter electrode layer 28, and hence the whole device.

Typical results for the optical measurements of the electrochromicdevice are shown in FIG. 4, where the measured transmission is plottedas a function of the amount of intercalated lithium. The percenttransmission, which is dominated by the absorption of the counterelectrode, starts out low and increases as the charge, in the form oflithium ions, is intercalated. At higher levels of intercalated lithium,the transmission proceeds through a maximum and then begins to decreasewhen additional lithium is added beyond the maximum. The amount ofcharge necessary to obtain the maximum transmission of the device,measured in-situ, is utilized as a process control parameter to ensurethe correct level of lithium is deposited, and ultimately intercalatedonto or into the mixed tungsten-nickel oxide film.

It should also be noted that the starting transmission for the counterelectrode depends on the thickness of the mixed tungsten-nickel oxidefilm and the absorption coefficient, which is dependent on thetungsten-nickel ratio and the oxidation state of the material. Moreover,it has been shown that a higher transmission is obtained for a moretungsten rich film and also for a more reduced film.

In another embodiment, the amount of lithium deposited onto the counterelectrode layer 28 is in excess of the amount required to achieve themaximum transmission, such that the greatest transmission is stillachieved as and when the excess lithium is lost during subsequentprocessing steps. If excess lithium is deposited, such amount of excesslithium ranges from about 10% to about 40% above that required toachieve the maximum transmission. The amount of excess lithium added,however, ultimately depends on the CE layer 28 thickness and therequirements for the electrochromic device's performance.

A second conductive layer 24 is deposited on the lithiated CE layer 28by methods well known in the art and as described above in thedeposition of the first conductive layer 26.

The device is completed by heating the entire electrochromic device in avacuum, an inert atmosphere, or an atmospheric oven. It has beendetermined that in order to obtain a suitably uniform device afterprocessing, there is a trade-off between the heating time and the size,e.g. larger windows require a longer time to heat up. It is alsoobserved that the process can be achieved by heating at a lowertemperature for a shorter time. In other words, there appears to be arequirement that the time-temperature product is approximately constant.Devices with sizes suitable for use in glazing products should be heatedto a temperature ranging from about 280° C. to about 500° C., preferablyto a temperature ranging from about 355° C. to about 395° C. The devicemay be heated for a time ranging from about 1 minute to about 120minutes, preferably from about 10 minutes to about 30 minutes. Smallerdevices, for other applications such as variable transmission filtersfor cameras and the like, can be heated much more rapidly, as thestringent requirements for uniformity are somewhat reduced.

In another embodiment, the device can be heated prior to the secondconductive layers being deposited. This method results in electrochromicdevice properties substantially the same as those discussed in thepreceding embodiment, but allows for the heating to be done in the sameprocess chamber as the deposition, possibly resulting in improvedprocess flow.

The heat treatment process has a positive effect on the switchingcharacteristics of the electrochromic device, as well as improving theconductivity and transparency of the second conductive layer 26. Theheat treatment also has the effect of increasing the transmission of thelithiated CE layer 28.

As already mentioned, the position of the complementary counterelectrode layer 28 and the electrochromic layer 30 may be reversed inthe overall structure presented in FIG. 3. One skilled in the art wouldappreciate that should the layers be reversed, the method ofmanufacturing the device does not change with regard to the steps thathave to be performed to generate each layer. Regardless of the order ofsteps performed to form an electrochromic device employing theaforementioned complementary counter electrode, the device may still besubjected to the heat treatment process described herein.

One skilled in the art would appreciate that the methods utilized aboveto create a complementary counter electrode comprised of a mixedtungsten-nickel oxide may be used to develop a counter electrode for usein connection with any electrochromic device. That is, the methods usedto develop the complementary counter electrode are not limited to use inthe specific electrochromic device discussed herein. Moreover, themethod of making the complementary counter electrode discussed above mayalso be used to deposit a complementary counter electrode on anysurface, not merely ion conductor layers or other conductive layers.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method for the preparation of an electrochromic device comprising: a) providing a first conductive layer, b) depositing one of an electrochromic layer or a counter electrode layer comprising a mixed tungsten-nickel oxide on said first conductive layer, thereby providing a first deposited electrode, c) depositing an ion-conductor layer on said first deposited electrode, d) depositing the other of said electrochromic layer or said counter electrode layer on said ion-conductor layer, thereby providing a second deposited electrode, e) depositing a second conductive layer on said second deposited electrode, f) heating said electrochromic device, and g) depositing lithium onto said counter electrode layer whereby said mixed tungsten-nickel oxide is reduced.
 2. The method of claim 1, wherein an amount of nickel in said mixed tungsten-nickel oxide ranges from about 15% to about 90% by weight of said mixed oxide.
 3. The method of claim 2, wherein said amount ranges from about 30% to about 70% by weight of said mixed oxide.
 4. The method of claim 2, wherein said amount ranges from about 40% to about 60% by weight of said mixed oxide.
 5. The method of claim 1, wherein said electrochromic layer comprises a metal oxide.
 6. The method of claim 5, wherein said metal oxide is selected from the group consisting of tungsten oxide, vanadium oxide, molybdenum oxide, niobium oxide, titanium oxide, iridium oxide, chromium oxide, copper oxide, and manganese oxide.
 7. The method of claim 5, wherein said metal oxide is doped with one or more metals.
 8. The method of claim 1, comprising depositing said lithium in an amount which provides a maximum transmission through said counter electrode layer.
 9. The method of claim 1, comprising depositing said lithium in an amount in excess of said amount which provides a maximum transmission through said counter electrode layer.
 10. The method of claim 9, wherein said excess amount ranges from about 10% to about 40% above said amount which provides a maximum transmission through said counter electrode layer.
 11. The method of claim 1, comprising heating said electrochromic device to a temperature ranging from about 280° C. to about 500° C.
 12. The method of claim 11, comprising heating said electrochromic device to a temperature ranging from about 355° C. to about 395° C.
 13. The method of claim 1, comprising depositing said counter electrode layer by means of physical vapor deposition.
 14. The method of claim 1, comprising depositing said counter electrode layer by means of intermediate frequency reactive sputtering.
 15. The method of claim 1, comprising depositing said counter electrode layer by means of DC sputtering.
 16. The method of claim 1, comprising depositing said lithium on said counter electrode layer by means of wet chemical methods.
 17. The method of claim 1, comprising depositing said lithium on said counter electrode layer by means of physical vapor deposition.
 18. A method of making a counter electrode layer for use in connection with an electrochromic device comprising: a) depositing a film of mixed tungsten-nickel oxide on a substrate, b) reducing said mixed tungsten-nickel oxide film by depositing lithium on said film, and c) heating said counter electrode layer.
 19. The method of claim 18, wherein an amount of nickel in said mixed tungsten-nickel oxide ranges from about 15% to about 90% by weight of said mixed oxide.
 20. The method of claim 19, wherein said amount ranges from about 30% to about 70% by weight of said mixed oxide.
 21. The method of claim 19, wherein said amount ranges from about 40% to about 60% by weight of said mixed oxide.
 22. The method of claim 18, comprising depositing said lithium in an amount which provides a maximum transmission through said counter electrode layer.
 23. The method of claim 18, comprising depositing said lithium in an amount in excess of said amount which provides a maximum transmission through said counter electrode layer.
 24. The method of claim 23, wherein said excess amount ranges from about 10% to about 40% above said amount which provides a maximum transmission through said counter electrode layer.
 25. The method of claim 18, comprising depositing said counter electrode layer by means of physical vapor deposition.
 26. The method of claim 18, comprising depositing said counter electrode layer by means of intermediate frequency reactive sputtering.
 27. The method of claim 18, comprising depositing said counter electrode layer by means of DC sputtering.
 28. The method of claim 18, comprising depositing said lithium on said counter electrode layer by means of wet chemical methods.
 29. The method of claim 18, comprising depositing lithium on said counter electrode layer by means of physical vapor deposition. 